Radio communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such communication networks generally support communications for multiple user equipments (UEs) by sharing available network resources. One example of such a network is the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology standardized by the 3rd Generation Partnership Project (3GPP). UMTS includes a definition for a Radio Access Network (RAN), referred to as Universal Terrestrial Radio Access Network (UTRAN). The UMTS, which is the successor to Global System for Mobile Communications (GSM) technologies, supports various air interface standards, such as Wideband Code Division Multiple Access (WCDMA), Time Division-Code Division Multiple Access (TD-CDMA), and Time Division-Synchronous Code Division Multiple Access (TD-SCDMA). The UMTS also supports enhanced 3G data communications protocols, such as High Speed Packet Access (HSPA), which provides higher data transfer speeds and capacity to associated UMTS networks. As the demand for mobile broadband access continues to increase, research and development continue to advance the UMTS technologies not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications. For example, UMTS based on WCDMA has been deployed in many places around the world. To ensure that this system remains competitive in the future, 3GPP began a project to define the long-term evolution of UMTS cellular technology. The specifications related to this effort are formally known as Evolved UMTS Terrestrial Radio Access (EUTRA) and Evolved UMTS Terrestrial Radio Access Network (EUTRAN), but are more commonly referred to by the name Long Term Evolution (LTE). The corresponding specifications for the core network side are commonly referred to as System Architecture Evolution (SAE) or Evolved Packet Core (EPC) (where EPC according to the most common definition is a subset of SAE). Together, SAE and LTE/EUTRAN form a complete cellular system referred to as Evolved Packet System (EPS).
A currently popular vision of the future development of the communication in radio communication networks comprises huge numbers of relatively small autonomous devices, which typically, more or less infrequently (e.g. once per week to once per minute) transmit and receive only small amounts of data (or, alternatively, are polled for data). These devices are typically not assumed to be associated with humans, but are rather sensors or actuators of different kinds, which communicate with application servers (which configure the devices and receive data from them) within or outside the cellular radio network. Hence, this type of communication is often referred to as machine-to-machine (M2M) communication and the above-mentioned devices may be denoted communication devices (CDs), or machine device (MDs). In the 3GPP standardization, the corresponding alternative terms are machine type communication (MTC) and machine type communication devices (MTC devices), with the latter being a subset of the more general term UE. FIG. 1 illustrates a 3GPP reference network architecture for MTC, which can be found in 3GPP TS 23.682 V.11.3.0.
With the nature of MTC devices and their assumed typical uses follow that these devices will often have to be relatively energy efficient, since external power supplies will often not be available. Also, it is neither practically nor economically feasible to frequently replace or recharge their batteries. In some scenarios, the MTC devices may not even be battery powered, but may instead rely on energy harvesting, e.g. gathering energy from the environment, that is, utilizing (the often limited) energy that may be tapped from sun light, temperature gradients, vibrations, etc.
A mechanism that has been introduced in 3GPP networks to conserve UE energy is Discontinuous Reception (DRX), which has been specified for both idle and connected mode. This mechanism allows a UE to spend most of the time in an energy efficient low power mode, often called sleep mode, while waking up to listen for pages in idle mode DRX or downlink resource assignments (i.e. downlink transmissions) in connected mode DRX only on specific occasions.
A DRX cycle generally comprises of a sleep period followed by an active period (although the occasions when the UE listens for pages in idle mode DRX are sometimes not referred to as “active periods” but rather “paging occasions”) and this cycle is generally repeated until the device is detached from the network or switches (in either direction) between idle and connected mode. Typically, but not necessarily, the sleep period is longer than the active period. A DRX cycle may have a more complex structure than described above, but for the purpose of this disclosure, the simplified DRX cycle description suffices (see e.g. chapter 5.7 of 3GPP TS 36.321 V11.3.0 for details on the connected mode DRX in LTE). Currently the maximum DRX cycle length for both idle mode DRX and connected mode DRX is 2.56 seconds (i.e. 256 subframes of one millisecond each). However, in order to make the DRX mechanism even more effective for energy deprived MTC devices, 3GPP is considering extending the maximum DRX cycle length, and thus the sleep period, both for idle mode DRX and connected mode DRX, leveraging the delay tolerance and infrequent communication need of many MTC applications. As the term Discontinuous Reception implies, it concerns only the downlink, whereas a UE may initiate communication in the uplink at any time, irrespective of the DRX cycle.